Thomas Leo Ogren's war on allergy-triggering plants spans almost three decades.

Ogren has seen grown men laid low by a sniff of a flower, taken chain saws to allergenic male yew pines, and burned out the motors of electric typewriters trying to get the word out. Before his first book on plant allergies was published in 2000, he collected more than 300 rejection slips.

But times have changed, and his new book, "The Allergy-Fighting Garden: Stop Asthma and Allergies with Smart Landscaping" (Ten Speed Press), is earning a good early reception from allergists as far away as Mongolia.

"I've been getting the feeling in the last two weeks that I'm suddenly about to be discovered or something," Ogren says with a chuckle.

"In the past, I couldn't send somebody an e-copy of (a book) prior to publication, and I didn't have things like LinkedIn, where I've been able to get to hundreds of doctors, so I'm taking advantage of it. I've just been going nonstop in the last couple of weeks and I'm getting this huge response from doctors, particularly pediatric allergists, all around the globe. Some places now, I'm getting (book) requests from them. I'm getting things from doctors (asking), 'What can we do to help?' That is really different."

Ogren, a horticulturist in San Luis Obispo, Calif., started investigating allergy-triggering plants because his wife of 48 years, Yvonne, has allergies and asthma.

"We'd walk under a particular tree, and she'd just immediately start sneezing," Ogren says. He started looking for a book on plant-triggered allergies, he says, but people just laughed. Using techniques like sniff tests, he found that some common garden plants triggered terrible allergies, whereas others did not.

Ogren began to get invitations to speak at garden clubs, and he decided to take pictures of pollen-producing male trees and pollen-free female trees. He started with local ash trees, and he was surprised to discover it was nearly impossible to find a female ash. The same was true of willows. Female trees — which help remove pollen from the air — were scarce or virtually nonexistent.

Gardeners, landscapers and homeowners prefer the male trees because they are viewed as less messy, he says. But they're also sources of allergenic pollen.

He also noticed that when it comes to seasonal allergies, proximity counts. Pollen exposure next to a tree can be 100 times greater than it would be a few houses away, so, if you suffer from allergies, it makes sense to remove the worst offenders from your yard.

The male yew (Taxus) and yew pine (Podocarpus) have highly allergenic pollen and rank a 10 out of 10 (the worst score) on Ogren's plant allergy scale. Female yews and yew pines, on the other hand, are very low-allergy, rating only 1 out of 10.

"We'll get out there and get the chain saw and cut that (male yew pine) down and plant (a female) in its place, and people will start getting better," Ogren says. "It's just like magic."

Ogren ranks more than 3,000 flowers, trees and shrubs for their allergy potential in his new book. He considers an array of factors, including not just the amount of pollen produced, but its potency, the size of the pollen grains, and whether the sap of the plant causes dermatitis.

Ogren says there's a lot more work to be done: He would like to see horticulturists develop pollen-free lawns, for instance. But he's happy to report victory on the home front: His wife's allergies are much less intense, and she has been free of asthma symptoms for almost 10 years.